Chemical sensing apparatus and methods
First Claim
1. Apparatus for indicating the end of service life of a filter cartridge for removing vapors of a chemical species from respired air, including a sensor that comprises:
- a polymer whose physical structure changes upon exposure to said chemical species,discrete electrically conductive elements at least partly separated by said polymer, andan impedance-measuring means for measuring the impedance between two of said conductive elements,wherein a change in said polymer'"'"'s physical structure upon exposure to said chemical species results in an increase in the impedance between said two conductive elements, andwherein the change in physical structure consists of partial or complete disintegration of said polymer.
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Accused Products
Abstract
Apparatus for the detection of a vapor of a selected chemical substance includes a sensor whose impedance changes upon exposure to such a vapor. The sensor comprises a polymer whose physical structure is altered by the vapor, e.g., through expansion or disintegration, and electrically conductive elements that are interspersed with or separated by the polymer. The interspersed elements may consist of a fine powder of carbon or of a metal in a matrix of silicone or other vapor-sensitive polymer. The electrical contacts between the powder particles are weakened when the polymer swells or disintegrates, which results in increased resistance. Alternatively, the capacitance between two conductive layers separated by a polymer layer decreases, and hence the impedance increases, when the polymer swells upon exposure to the vapor. In yet another embodiment, the polymer exerts a stress on a piezoresistive element and the stress is increased when the polymer swells, which causes a further increase in resistance. The changes are measured by an impedance-measuring circuit, such as a Wheatstone bridge.
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Citations
26 Claims
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1. Apparatus for indicating the end of service life of a filter cartridge for removing vapors of a chemical species from respired air, including a sensor that comprises:
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a polymer whose physical structure changes upon exposure to said chemical species, discrete electrically conductive elements at least partly separated by said polymer, and an impedance-measuring means for measuring the impedance between two of said conductive elements, wherein a change in said polymer'"'"'s physical structure upon exposure to said chemical species results in an increase in the impedance between said two conductive elements, and wherein the change in physical structure consists of partial or complete disintegration of said polymer.
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2. Apparatus for indicating the end of service life of a filter cartridge for removing vapors of a chemical species from respired air, including a sensor that comprises:
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a polymer whose physical structure changes upon exposure to said chemical species, electrically conductive elements interspersed within and at least partly separated by said polymer, and an impedance-measuring means for measuring the impedance between two of said conductive elements, wherein a change in said polymer'"'"'s physical structure upon exposure to said chemical species results in a change in the impedance between said two conductive elements, and wherein said conductive elements comprise two spaced electrical contacts on an electrically insulating substrate, said contacts being electrically connected to, and bridged by, a layer of said polymer admixed with a multiplicity of said conductive elements. - View Dependent Claims (3, 4, 5, 6, 7, 8, 9, 10)
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11. Apparatus for indicating the end of service life of a filter cartridge for removing vapors of a chemical species from respired air, including a sensor that comprises:
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a polymer whose physical structure changes upon exposure to said chemical species, electrically conductive elements at least partly separated by said polymer, and an impedance-measuring means for measuring the impedance between two of said conductive elements, wherein a change in said polymer'"'"'s physical structure upon exposure to said chemical species results in an increase in the impedance between said two conductive elements and wherein said conductive elements form two substantially parallel layers separated by said polymer, one of said layers having a vapor-permeable structure permitting permeation of vapor to said polymer.
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12. Apparatus for indicating the end of service life of a filter cartridge for removing vapors of a chemical species from respired air, including a sensor that comprises:
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a polymer whose physical structure changes upon exposure to said chemical species, electrically conductive elements at least partly separated by said polymer, and an impedance-measuring means for measuring the impedance between two of said conductive elements, wherein a change in said polymer'"'"'s physical structure upon exposure to said chemical species results in a change in the impedance between said two conductive elements, and wherein said conductive elements comprise two spaced electrical contacts on an electrically insulating base, said contacts being bridged by a vapor-permeable conductor that is separated from said base by said polymer.
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13. Apparatus for indicating the end of service life of a filter cartridge for removing vapors of a chemical species from respired air, including a sensor that comprises:
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a polymer whose physical structure changes upon exposure to said chemical species from said air, discrete electrically conductive elements at least partly separated by said polymer, and an impedance-measuring means for measuring the impedance between two of said conductive elements, wherein a change in said polymer'"'"'s physical structure upon exposure to said chemical species results in a change in the impedance between said two conductive elements, wherein said polymer appertains to the family of polymers that consists of ethylene propylene polymer, styrene butadiene resin, polybutadiene, isobutylene-isoprene polymer, chloroprene polymer, fluorocarbon polymer, and polyacrylate.
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14. Apparatus for indicating the end of service life of a filter cartridge for removing vapors of a chemical species from respired air, including a sensor that comprises:
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a polymer whose physical structure changes upon exposure to said chemical species from said air, discrete electrically conductive elements at least partly separated by said polymer, and an impedance-measuring means for measuring the impedance between two of said conductive elements, wherein a change in said polymer'"'"'s physical structure upon exposure to said chemical species results in a change in the impedance between said two conductive elements, wherein said sensor is a first sensor and further comprising a second sensor similar to said first sensor exposed to substantially the same temperatures and humidities, only one of the two sensors being accessible to vapor of said chemical species, wherein said polymer in one of said sensors is covered by a selectively permeable membrane, said membrane being permeable to water vapor but not to said chemical species.
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15. Apparatus for indicating the end of service life of a filter cartridge for removing vapors of a chemical species from respired air, including a sensor that comprises:
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a polymer whose physical structure changes upon exposure to said chemical species from said air, discrete electrically conductive elements at least partly separated by said polymer, and an impedance-measuring means for measuring the impedance between two of said conductive elements, wherein a change in said polymer'"'"'s physical structure upon exposure to said chemical species results in a change in the impedance between said two conductive elements, wherein said polymer is covered by a selectively permeable membrane that is permeable to said chemical species but not to water vapor, and wherein said membrane comprises a fluorinated polymer. - View Dependent Claims (16)
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- 17. A method of producing a sensor for detecting vapors of a chemical species which comprises bringing a polymer whose physical structure changes upon exposure to said chemical species into firm adhesive and electrical contact with an electrically conductive element, wherein said conductive element is affixed onto an electrically insulating base and coated with a layer of said polymer.
Specification